Allergy symptoms, or something else?

What allergy actually produces

Depending on where the reaction happens, allergy causes a fairly short list of things: sneezing and a blocked or running nose; red, itchy, watering eyes; an itchy rash or hives; swelling, typically of the lips or eyelids; wheeze and shortness of breath; and in the gut, pain, vomiting or diarrhoea. In its most serious form it causes anaphylaxis, which is covered under what an allergy is along with the mechanism behind all of this.

The difficulty is that none of those symptoms belongs to allergy alone. Every one of them has other common causes, which is why guessing produces so much wasted treatment — and why the useful question is usually not “what are the symptoms of allergy” but “is this one of them, or is it something else”.

The most useful single clue

Itch. Of all the features, itching is the one that points most reliably towards an allergic cause — itchy eyes, an itchy nose, an itchy palate or throat, itchy skin. Infections and irritants produce soreness, pain, pressure and congestion, but they do not usually itch.

The second clue is pattern. Allergy follows exposure, so it repeats: the same circumstances, the same time of year, the same room, the same animal, the same food. Symptoms that come and go for no discernible reason over months are less likely to be allergic than people assume.

Allergy or a cold?

This is the commonest confusion, and the two are genuinely similar at the start.

A cold is caused by a virus. It tends to build over a day or two, often begins with a sore throat, may come with a mild fever and aches, produces discharge that thickens and discolours as it goes on, and runs its course in roughly a week to ten days.

Allergic rhinitis begins within minutes of exposure rather than building over days, produces sneezing in runs, keeps the discharge thin and clear, and itches. There is no fever. It persists as long as the exposure does, which may be a season or, with an indoor allergen, indefinitely.

The giveaway is usually duration and itch together. A fortnight of symptoms with no fever and plenty of itching is not a cold, whatever it looked like on the first day. Equally, one episode in January with a sore throat and a temperature is not hay fever.

Rhinitis that is not allergic

This one is widely missed. It is entirely possible to have persistent rhinitis — blocked nose, running nose, postnasal drip — with no allergy involved at all, and allergy testing comes back negative because there is nothing to find.

Non-allergic rhinitis responds to things that are not allergens: changes in temperature, going from cold air into a warm room, strong smells, perfume, smoke, alcohol, spicy food, and hormonal changes including pregnancy. The symptoms are much the same as the allergic kind, although itching and eye involvement tend to be less prominent.

It matters because the management is not identical and because the hunt for an allergen is futile. A good deal of fruitless rearranging of houses and eliminating of foods is done by people whose rhinitis was never allergic.

The nasal spray trap

A particular and very common cause of a permanently blocked nose deserves singling out, because it is self-inflicted, easily missed and entirely reversible.

Decongestant nasal sprays work by shrinking the blood vessels in the nose, and they work well for a few days. Used beyond that, they produce rebound congestion: the nose blocks up again as each dose wears off, which prompts another dose, and the eventual state is worse than the original problem. The packs specify a short limit for exactly this reason, and it is worth observing. The distinguishing feature is that this affects the nose only, with no itching and no eye symptoms. It settles on stopping, though tapering is easier than stopping abruptly.

One crucial distinction, because conflating the two causes real harm: this applies to decongestant sprays, not to steroid nasal sprays. Steroid sprays do not cause rebound congestion — they are the treatment of choice for allergic rhinitis, they are intended for continuous daily use, and they are in fact one of the treatments used to get someone off a decongestant spray. Abandoning a steroid spray out of a general worry about “nasal spray addiction” means giving up the most effective treatment available for the wrong reason.

Sinusitis

Facial pain or pressure around the cheeks, eyes or forehead, a reduced sense of smell, thick discoloured discharge, toothache in the upper jaw and pain on bending forward point to sinusitis rather than allergy — though allergic rhinitis can lead to it, so the two are often found together.

Allergy on its own does not usually cause significant facial pain, and it does not cause fever.

Skin: allergy, irritation, or neither

A rash is the symptom most often attributed to allergy and least often caused by it.

Where skin has been in contact with something, the question is whether the reaction is allergic or simply irritant — the latter being commoner, not immune-mediated, and capable of affecting anyone with enough exposure. Contact dermatitis covers the distinction and why it changes what is worth doing.

Hives are the other common assumption. Raised, itchy weals that move around and individually fade within a day are indeed hives — but hives are frequently not allergic at all, and in children they most often follow a viral infection. Hunting for a food trigger is the usual first instinct and usually the wrong one.

Eczema, fungal infections, heat rash, and the many ordinary viral rashes all get blamed on allergy regularly.

Gut symptoms

Pain, bloating, wind and diarrhoea after eating are far more likely to be intolerance than allergy. Intolerance does not involve the immune system, is dose-related, and is not dangerous; food allergy involves IgE, can be triggered by a trace, and can be severe.

Coeliac disease is a third thing again — neither allergy nor intolerance, but an autoimmune condition — and it is worth knowing that testing for it requires gluten still to be in the diet, so cutting it out before being tested makes the diagnosis harder rather than easier.

Asthma is not an allergy

Allergy is one of the commonest triggers for asthma, but asthma is a condition in its own right, and it is also set off by exercise, cold air, infections, smoke and stress. Treating the allergy helps where allergy is the trigger; it does not replace managing the asthma, which needs its own review, inhalers and written plan.

Sorting it out

Most of the answer comes from the history rather than from tests: what happened, how quickly, how long it lasted, whether it has happened before, and what was different about those occasions. Keeping a note over a few weeks of when symptoms appear and what preceded them is more useful than it sounds, and more useful than most tests on their own.

Testing has a part to play, read alongside that history — and the reason it is read alongside rather than on its own is that a positive result indicates sensitisation rather than allergy, and a negative one is the more informative of the two.

A pharmacist is a reasonable first stop. A GP is worth seeing where symptoms persist despite treatment, where they are affecting sleep, work or school, where breathing is involved, or where it simply is not clear what is going on — which, given everything above, is a perfectly good reason to ask.